1. Field of the Invention
This invention relates to a key telephone system and more particularly to a key telephone system so configured that registration of system data in a key service unit or alteration of system data are effected easily.
2. Description of the Prior Art
The conventional key telephone system, as widely known, comprises a key service unit and a plurality of key telephone sets connected to the key service unit through connecting cables. In recent years, adoption of electronic devices in the key telephone systems of this class has advanced to a point where their key service units incorporate therein, as a control circuit, a microcomputer (CPU) adapted to effect various controls.
This electronic control circuit is composed of a control circuit (CPU), a read-only memory (ROM) serving to provide the control circuit (CPU) with a program, a random access memory (RAM) functioning to store necessary data and specifying work areas, and various buses such as data bus, address bus, and control lines.
In the key telephone system of the kind incorporating electronic devices as described above, various data are transmitted and received during the transfer of information between the key service unit and the individual key telephone sets. Broadly, these data are classified as being one of the following three kinds.
(1) Control data (control program data) based on the programs forming the foundation of a given system which are of a permanent nature.
(2) General system data established for a given system based on such system functions as setting telephone sets so as to be capable of issuing a sound on reception of a call, setting the dial pattern (DP/MF) of an office line introduced to the key service unit, and setting calender and clock (hereinafter referred to as "system data").
(3) Individual system data established by, and subject to change by, an individual user in conformity with conditions of use, places of installation, and methods of use on the part of the user, as in assigning numbers (such as *01) for abbreviated dialing, setting dial data corresponding to the assigned numbers, and setting the day-night switch of service class, for example (hereinafter referred to as "user data").
The control data are characteristic of a given system and absolutely invariable. They are fixed in form at the time that the system is shipped as a product from the factory. The system data are such that when a user places an order for a key telephone system including a specification for example such that all the key telephone sets are to be adapted to issue a sound on reception of a call, the data are established to conform with the user's order at the time that the system is shipped as a product or at the time that the system is installed in the user's office. The user data are such that, after the system has been installed at a user's office, the data can be freely altered to suit the user's own convenience at any time he pleases.
It has been customary in the conventional key telephone system of this class to have data concerning functions, i.e. system data such as the kind of system, data established to control system functions (system constants) and data with information on the classification of circuits, registered in a random access memory RAM.
When the system data are required to be altered or re-registered during the use of the key telephone system, the person handling the system is required to stop the operation of the system temporarily and then proceed to effect the alteration or re-registration of system data.
As described above, tne conventional key telephone system has entailed the disadvantage that numerous pieces of system data must be registered one by one after the work of wire distribution is completed and, therefore, the registration of system data consumes much time. When the system data are required to be altered or re-registered while the key telephone system is in use, the key telephone system must be temporarily stopped to permit the alteration or re-registration of system data. If this stop of the key telephone system is protracted, it will inconvenience the user's business operation.
Further, when a static RAM is employed as the RAM mentioned above, the system requires use of a backup battery for protection of data during possible power failure. The incorporation of this battery proves costly when the RAM data capacity is large and, as a natural consequence, the battery is required to have a large capacity.